1. Field of the Invention
The present invention relates to photoelectrophoretic migration imaging and in particular to apparatus for implementing such imaging in response to electronic signals representative of an original.
2. Description of the Prior Art
Photoelectrophoretic migration imaging involves the light image exposure of a liquid suspension, comprising dielectric liquid carrier and photoconductive toner particles, while between two electrodes that provide a migration inducing field. U.S. Pat. No. 3,140,175 to Kaprelian discloses early procedures and apparatus of this type. In operation, the suspended toner particles attain a charge and migrate from the suspension to one of the electrodes. Upon exposure the illuminated particles migrate to the other electrode in accordance with the exposing light image pattern. Various embodiments for photoelectrophoretic migration imaging have been subsequently proposed (see, e.g., Tulagin, U.S. Pat. No. 3,384,565). Recently a photoimmobilized electrophoretic migration imaging method has been described wherein the light-exposed, photoconductive toner particles are retained at the electrode to which they first migrate and unexposed particles change charge and migrate to the other electrode (see, e.g., U.S. Pat. No. 3,976,485).
Certain difficulties have arisen during efforts to commercialize such photoelectrophoretic migration imaging systems. For example, high density images are difficult to attain in such systems. Further, in color imaging using this technique, it would be useful to have capabilities for color adjustment. Since the image density is dependent in part on light intensity, filtering to achieve color adjustment is not a desirable approach. Also, it is envisioned that office systems of the future may utilize image transmission, and it is not apparent how optically-addressed copiers of the type described above can accommodate such a future need.
In view of one or more of the problems and/or desired capabilities noted above, there have been described in literature proposals for electrically-addressable photoelectrophoretic imaging systems. For example U.S. Pat. No. 3,663,396 and British Pat. No. 1,341,690 respectively disclose electronic address of a color cathode ray tube and an electroluminescent panel used as the exposure source for such an imaging system. These approaches offer the potential for improved density, color adjustment and electronic transmission of images; however, the exposure elements are fragile and costly. The complicated control systems for addressing the exposure elements add another large factor of cost so that such proposed systems would be quite expensive.
A somewhat simpler approach is disclosed in U.S. Pat. No. 3,682,628 wherein a point light source is scanned, line by line, across the photoelectrophoretic suspension, through a transparent electrode. The opposite electrode is selectively energized, in accordance with a video signal representative of the image to be formed, and photoconductive particles in suspension are selectively activated on coincidence of the point light source and an energized condition of the electrode. However, this system cannot provide color separation, so that separate exposures of separate mono-particle suspensions to form three different color separation images (e.g., cyan, magenta and yellow) are required. This requires additional equipment and time as compared to conventional tri-particle suspension systems. Additionally, the procedure requires registry of three images during transfer, and such transfer is extremely difficult to accomplish accurately.